1. Field of the Invention
The present invention relates to heating devices, and particularly relates to a heating device which uses hot water to adjust the temperature of air blown into a vehicle passenger compartment by controlling the amount of hot water flowing therein using a flow control valve.
2. Description of Related Art
A method in which blown air temperature is controlled by controlling a flow amount of hot water to a heat exchanger is known in the art. In such an automotive air conditioner, a water pump driven by the automobile engine is used in a hot water circuit in which the hot water (engine cooling water) is circulated. Therefore, the rotational speed of the water pump fluctuates with fluctuations of engine rotational speed and hot water pressure to the heat exchanger fluctuates to a large degree. Because the fluctuation is a factor of fluctuation of the temperature of the blown air to the heat exchanger, the fluctuation of the hot water pressure causes the hot water flow amount to the heat exchanger to fluctuate.
A hot water-type heating device for controlling the fluctuation of the blown air temperature of the heat exchanger is disclosed in Japanese Patent Application Laid-Open No. Hei 8-121627. This device includes a heat exchanger for heating air by exchanging heat between hot water supplied from a water-cooled type engine for traveling and air, a flow control valve for controlling a flow amount of the hot water supplied to the heat exchanger from the engine and a bypass circuit for allowing hot water to flow therethrough while bypassing the heat exchanger.
A pressure-responsive valve for increasing the opening degree of the bypass circuit corresponding to a pressure rise of the hot water supplied from the engine and a variable restricting valve which moves in response to the movement of the pressure-responsive valve are provided in the bypass circuit. Therefore, the opening degree of the water passage for the hot water passing through the heat exchanger is reduced at the variable restricting valve as the pressure-responsive valve increases the opening degree of the bypass circuit.
Therefore, when the supply pressure of the hot water from the engine rises, the opening degree of the bypass circuit is increased by the pressure-responsive valve and the opening degree of the heat exchanger passage is reduced by a variable restricting valve, and an increase of the amount of flowing hot water to the heat exchanger can be limited to a small value. Thus, fluctuation of the blown air temperature of the heat exchanger can be restrained to a small range with respect to wide-ranging changes of the hot water supply pressure.
In the related art described above, however, because a variable restricting valve other than the pressure-responsive valve is additionally disposed with respect to the flow control valve, a size of the valve device portion of the hot water-type heating device becomes large and the number of components increases, and a corresponding increase in cost cannot be prevented. Further, an operational malfunction of the valve due to deformation or the like of a shaft can occur in a moving mechanism between the pressure-responsive valve and the variable restricting valve.